Variable frequency motor drives offer a number of potential benefits for applications such as driving compressors or other loads for heating, ventilation, air-conditioning, or refrigeration (HVACR) systems, including potential for enhanced efficiency, power density, and speed control precision. Such motor drives also present unique challenges with respect to robustness, service life, and tolerance to rated voltages including low input line voltages within a rated range. Heretofore, HVACR drive and motor designs have faced a number of undesirable trade-offs. For example, in selecting DC bus capacitor components there are competing needs for service life and robustness, and sufficient capacitance to meet voltage ripple and harmonic feedback mitigation goals. Traditionally, electrolytic capacitors have been utilized in the DC bus to provide the desired level of capacitance, however, their limited service life relative to the lifespan of HVACR systems has long been a source of frustration for designers and consumers. Some recent designs have utilized film capacitors which offer significantly enhanced lifespan compared to electrolytic capacitors; however, this benefit comes at a cost of lower capacitance relative to electrolytic capacitors.
The aforementioned trade-offs are compounded by the need to account for rated input line voltage phenomena. Utility power lines and other power sources have a rated voltage range which is sometimes expressed as a nominal rated voltage with the range being implicit. Power electronics and motor drive systems coupled to such power sources must be configured to meet desired performance criteria over the full rated input voltage range, including the low voltage portion of the rated range, as is expected that such voltages will be encountered in normal real world operation. This presents a unique challenge to HVACR compressor drives which must be designed to maintain a desired speed to attain desired performance and efficiency. Lower capacitance drives produce lower output voltages and are more susceptible to performance variation from input voltage variation. This in turn forces system designs toward motors with lower electrical constants which require greater current to achieve functional requirements. This increases the expense both of the system itself and of operating the system. Increased current also increases losses through resistive heating which further compromises operational efficiency. Conventional attempts to address these and other challenges suffer from a number of shortcomings. There is a need for the unique and inventive apparatuses, methods and systems disclosed herein.